The present invention relates generally to the field of electrical circuit interrupter devices, such as circuit breakers, motor protectors and the like. More particularly, the invention relates to a method and apparatus for interrupting current in more than one phase of a multiphase circuit in response to an overcurrent or other trip condition occurring in one of the phases.
A considerable array of devices and methods are known for interrupting electrical power between conductors. Such devices include circuit breakers of various design and construction, electric motor protectors, and other overcurrent protective devices. In general, such devices provide a path for the flow of electrical power under normal operating conditions, and a mechanism for breaking the current path in the event of an actual or anticipated overcurrent, overtemperature, or other undesirable condition. The current path is typically established by a movable element, such as a pivotable arm carrying a first contact region, and a stationary conductor coupled to a second contact region. The contact regions are brought into contact with one another during normal operation, permitting electrical power to flow through conductors coupled to the first and second contact regions. A sensing device or actuator detects fault conditions and triggers movement of the arm to separate the contact regions from one another, thereby interrupting the current path between the conductors. In multiphase devices of this type, a similar arrangement is provided for each phase. Moreover, in the latter case, a trip mechanism typically links the mechanical elements of each phase to ensure that power is interrupted in all phases in the event of a fault in a single phase. A toggle or catch mechanism is generally provided to guard against rebound of the movable arm and recontact of the conductive regions.
Other types of circuit interruption devices include arrangements in which a movable conductive bridge or spanner carrying a pair of contacts extends between two stationary contact regions. When the device is installed in service, source and load conductors are coupled to the stationary contact regions. The bridge serves to complete a current carrying path between the conductors in normal operation. For interruption of current an actuator or interrupt initiation device forces the bridge element away from the stationary contact regions, generating arcs between the separating regions as the bridge element is displaced. A circuit interrupter of this type is described in U.S. Pat. No. 5,579,198, issued on Nov. 26, 1996 to Wieloch et al.
In conventional circuit interrupting devices, such as circuit breakers, a mechanical or electromechanical assembly is associated with the movable contact support to catch or bias the contact support in a non-conducting position following a trip event and to retain the support in the non-conducting position until the device is manually or automatically reset. Common mechanical catch and retaining assemblies included toggle arrangements, snap-action structures and the like, designed to move rapidly to a retaining position following the trip event. An important function of such assemblies is to deploy with sufficient rapidity to prevent the movable contact from bouncing or returning to its conductive position, thereby re-establishing the current carrying path.
A goal of most circuit interrupter devices is to interrupt the current carrying path as quickly as possible in order to limit let-through energy and thereby to ensure the greatest protection for the load coupled to the device. As the response rates of interrupter designs is increased, however, the problem of catching and retaining the movable contact becomes increasingly more difficult. In particular, the retaining device must allow for extemely rapid opening of the electrical circuit, while intervening as quickly thereafter as possible to prevent the movable contact from rebounding. While advances have been made in trip and retaining devices that have enhanced their rapidity, response rates of such devices appear to be limited by their mass and complexity.
Additional difficulties in conventional multiphase circuit interrupter devices arise from the need to interrupt power to all phases upon the occurrence or the anticipated occurrence of a trip event in one phase. For example, in conventional multiphase circuit breakers and motor protectors, a trip event occurring in one power phase may result in rapid opening of the current carrying path for that phase, while the current carrying paths for the remaining phases will not be interrupted until a shared mechanical or electromechanical actuator assembly can be triggered to displace movable contacts for those phases. In the interim between the initial condition occurring in the first phase and the time at which the actuator mechanism pulls out the remaining phases, the load may be exposed to harmful current levels in the latter phases, potentially resulting in damage to the load.
There is a need, therefore, for an improved apparatus and method for interrupting current in multiphase electrical circuits upon the occurrence of a trip event in one of the phases. There is a particular need for a technique for rapidly causing displacement of movable elements in such power phases that does not rely directly on movement of a shared mechanical or electromechanical actuator assembly. The technique should ideally provide a device for maintaining the phases interrupted until a retention assembly can be displaced to hold the movable elements in their interrupted positions.